Russia and the United States have set a deadline of midnight Damascus time (2200 GMT) Friday for “the cessation of hostilities” between President Bashar al-Assad’s regime and rebel forces.

A cessation of hostilities in Syria came into effect at the agreed time of midnight on Saturday (2200 GMT Friday), under a U.S.-Russian plan whichwarring sides in the five-year conflict have said would to commit to.

Syria’s government and insurgents warring against it have said they would respect the halt to fighting.

The truce does not apply to ISIS and al Qaeda affiliate the Nusra Front, and the Syrian government and Moscow have said they will not halt combat against those militants.

The UN Security Council threw its weight Friday behind a ceasefire agreement for Syria and demanded that it be upheld.

The council unanimously adopted a resolution drafted by Russia and the United States that endorses the ceasefire deal and “demands that the cessation of hostilities to begin at midnight (Damascus time)” (2200 GMT).

UN envoy Staffan de Mistura said Friday Syria’s government and rebels will re-start peace talks on March 7 if a ceasefire holds and more aid is delivered.

Barely two hours before the Syria ceasefire was due to go into effect, the United States warned Russia that it was time to “put up or shut up.”

State Department deputy spokesman Mark Toner said Washington had received assurances from Moscow that it would not bomb the “moderate opposition” after the truce.

“I don’t know how to put it any better than saying: ‘It’s put up or shut up time,'” Toner told reporters.

“It is time for them to show through action rather than words that they are serious about what they profess to be serious about, which is a ceasefire, a cessation of hostilities and a political process that leads to a transition.”

As he spoke, intense Russian bombing of rebel bastions was continuing in Syria in the runup to the ceasefire.

Earlier in the day, Russia’s foreign minister said it expects the U.N. Security Council to back a resolution endorsing the planned ‘cessation of hostilities’ in Syria, but nobody can give a 100 percent guarantee that the ceasefire plan will be implemented.

Sergei Lavrov also used a news briefing to call on the Unites States and its allies to avoid “ambiguity” about any “Plan B” for Syria and to give up any idea of conducting a land operation there.

The U.N. Security Council voted Friday on a US-Russian draft resolution endorsing the Syria ceasefire.

The draft text welcomes the truce as “a step towards a lasting ceasefire” and endorses the U.S.-Russian agreement on the truce.

It “demands the cessation of hostilities to begin at midnight (Damascus time)” and renews a call to allow humanitarian aid to be delivered.

The measure urges all countries, in particular those involved in the Syrian peace process, to “use their influence with the parties to the cessation of hostilities to ensure fulfillment of those commitments.”

The deal is between President Bashar al-Assad’s regime and rebel forces, but excludes ISIS and the Al-Qaeda-linked Al-Nusra Front, which control large swaths of territory in Syria.

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